Explosion-resistant structure



Nov. 22, 1960 F. A. LOVING, JR

EXPLOSION-RESISTANT STRUCTURE Filed March 10. 1958 ill 71 I3 INVENTORFRANK ABRAHAM LOVING, JR.

ATTORNEY States Pate EXPLOSION-RESISTANT STRUCTURE Frank Abraham Loving,Jr., Wenonah, N.J., assignor to E. I. du Pont de Nemours and Company,Wilmington, Del., a corporation of Delaware Filed Mar. 10, 1958, Ser.No. 720,318

8 Claims. (Cl. 73-35) The present invention relates to anexplosion-resistant structure. More particularly, the present inventionrelates to a structure whereby undesirable effects of the detonation ofan explosive charge, i.e., noise, air blast, and missiles, can beeliminated.

The number of industrial applications other than blasting involving theuse of explosives is rapidly increasing. Such applications include thejoining of metal elements, for example by the method described in US.Patent 2,367,206 (Davis, to du Pont, January 16, 1945) and the use ofexplosives to emboss a metal. surface, which method is fully describedin US. Patent 2,604,042 (Cook, to Imperial Chemical Industries, July 22,1952). More recently, a U.S. Patent (2,703,297, MacLeod, March 1, 1955)has issued on a method for explosively hardening manganese steel. Theexplosive charges used in the aforedescribed applications may vary froma few grains to a hundred pounds. In all cases, adequate precautionsmust be taken to protect personnel and surroundings from any harmful orannoying effects of the actuation of the explosive, which precautions,of course, also must be taken in the experimental testing and developingof explosives.

Among these effects is included the noise characteristic of theexplosives detonation. Although the noise per se is seldom hazardous, itis frequently annoying to the point of being intolerable, especiallywhen the industrial or testing site is in a populated area. Very often,the noise produced in the operations results in delays and stoppage ofthe operations due to complaints concerning the noise. This problemnaturally could be resolved by conducting the operations in a remote andisolated location. However, this solution of the problem is not onlyinconvenient but also unfeasible in many industrial areas.

The other effects encountered in the use and testing of explosives,namely air blast, i.e. the airborne pressure pulse, and missiles,definitely constitute safety hazards. In order to protect personnel fromsuch hazards, resort often is made to the construction, at theindustrial or testing site, of massive barricades to contain theexplosion. Large barricades capable of withstanding the explosion ofcharges weighing up to 10 pounds are exceedingly expensive. Moreover,although they may be designed to arrest missiles and the air blastadequately, the barricades usually fail to prevent the objectionalnoise.

As is well known in the art, the noise, air blast, and missiles can beeliminated effectively by the detonation of an explosive under severalfeet of a liquid such as water. The liquid, which is highly compressibleat explosion pressures, efficiently absorbs the explosion energy whichthen is transmitted to the earth or other surrounding medium with aminimum effect on nearby surface installations. Moreover, as pointed outin the afore-mentioned MacLeod patent, the confinement afforded by theliquid often produces beneficial results in the operation.

Since natural reservoirs of water, i.e. small ponds or lakes, generallyare unavailable to the tester or operator,

2,960,859 Patented Nov. 22, 1960 artificial reservoirs must beconstructed. The use of small pits in the earth filled with water oranother liquid is unfeasible because of the destruction of the earthenwalls due to the explosion. The use of liquid-filled tanks ofconventional steel or concrete construction is equally unfeasiblebecause of the very damaging effects upon the steel or concrete wallsdue to the underwater pressure pulse. Because of the high absorption inthe liquid, e.g. water, of the energy from the explosion, at a givendistance the underwater pressure pulse is many times more destructivethan is the corresponding airborne pressure pulse. Although the use of aresilient material such as rubber would overcome some of thedisadvantages inherent in a conventional tank of steel or concrete, thefabrication of a rubber tank is impractical not only because of economicfactors but also because the preparation of a rubber tank of sufficientstiffness to hold its shape in the required sizes is diflicult if notimpossible. Thus, the very characteristics which make a liquid aneflicacious protection medium also make extremely difiicult andexpensive the construction of a tank or reservoir which will withstandthe underwater explosion pressure.

Accordingly, an object of the present invention is the provision of anefiicient means for the containment of the noise, pressure pulse, andmissiles produced by the actuation of an explosive. Another object ofthe present invention is the provision of an explosion-resistantstructure of simple and economical construction wherein a liquid, forexample water, is used as the protective medium. A further object of thepresent invention is the provision of a Water-filled structure for thecontainment of noise, pressure pulse, and missiles from an explosion,which structure is resistant to damage from the underwater pressurepulse resulting from the explosion and thus can be used over and overagain.

I have found that the foregoing objects may be achieved when I provide,as a reusable explosion-resistant structure for the testing and use ofexplosives, a pit within the earth, a reversibly expandable, i.e.capable of expanding and then returning to its original position,cylindrical liner within the pit, a fill of dense noncohesive materialbetween the walls of the liner and the vertical earthen walls of thepit, the fill extending from the bottom of the pit to occupy a portionof the space within the liner, and a body of liquid disposed within theliner and pit.

In accordance with the structure of the present invention, thereversibly expandable cylindrical liner comprises a plurality of rigidoverlapping elongated elements, for example steel plates, interconnectedin laminar form by a plurality of spaced, movable guiding and retainingmeans.

In order to illustrate the invention more completely, reference now ismade to the accompanying drawings in which: 7

Figure l is a side view showing partially in section theexplosion-resistant structure of the present invention.

Figure 2 is an end view of a segment of reversibly expandablecylindrical liner for use in the structure, the liner being constructedin accordance with one embodiment of the present invention, and

Figure 3 is an end view of a segment of a reversibly expandablecylindrical liner for use in the structure, this liner being constructedin accordance with another embodiment of the present invention.

Referring now to the figures in more detail, in Figure 1 showing thestructure, 1 is the earths surface, 2 represents the earthen wall of apit formed in the earth, 3 is a reversibly expandable cylindrical linerdisposed within the pit, 4 is dense, noncohesive material filling thespace between the liner 3 and the vertical walls 2 of the pit andextending from the bottom of the pit to occupy a portion of the spacewithin the liner, and 5 indicates the level of the liquid within theliner and pit. Liner 3 consists of a number of curved metal, e.g. steel,plates 6. Platesfi a re arranged to overlap in laminar form and are ctedby tie-rods 7, .the ends of which areenlar ged rm stop elements ,8. Thetie-rods 7 are inserted in centralapertures' in lugs 9 and which arewelded onto t is s s l In Figure 2, the segment of the cylindrical linershown eo'rresponds in form to the liner illustrated in Figure l, '6being the plates, 7 the tie-rods, 8 the stop elements, and 9 and 10 thelugs. In this embodiment, the plates over-lap to form an inner series ofplates and an outer series of plates. The edges of adjacent plates 6 inthe er layer approach each other in the region of the center oniqn of aplate 6 of the outer layer of plates, a slight gap being left betweenthe adjacent plates 6. At sp cedtnervns, a'lug 9 is welded on thecontacting surrace'ar'th central portion of the plate 6 of the outerlayer, "this'lug9 'thus being positioned in the gap between theadjacentplates 6 of the inner layer. A slightly"shorter lug'10' is welded to thenoncontacting surface of 'eachfof the adjacent plates 6 of the innerlayer, the lug 10 being attached a slight distance from the lateral edgeof "thepla'te. "Through the apertures in these three :iu'gs' is passedthe tie-rod 7, and then the appropriate stops 8 are fastened to each endof the tie-rod 7. This series of three lugs 10, 9, 10 and the tie-rod 7is repeated for every set of adjacent plates in both the inner and outerlayers of plate. The layers of steel plate, therefore, are held snuglytogether, the gaps between the plates in one layer being positioned nearthe center of the plates in the other layer.

".In the embodiment illustrated in Figure 3, the plates overlap in amanner such that every plate 6 on both its interior and exterior surfacecontacts another plate 6, the central portion of each plate 6 remainingfree of contact with any other plate. Iral, noncontacting portion ofeach plate 6 is fastened a lug l0, and a lug 9 is provided, on thenoncontacting surface, adjacent the edge of each plate 6. Through thislug 9 on the edge of every plate and thence through the adjacent lug 10provided on the central portion of the next plate is passed the tie-rod7 in the apertures provided in the lugs. The stops 28 then are fastenedto the ends of the tie-rod. This series of two lugs and a tie-rod isrepeated circumferentially around the liner and at given intervals alongthe vertical surfaces of the liner.' Thereby, the plates are held firmlytogether.

In operation, the explosive charge is actuated below surface of theliquid in the liner, and the resulting internal pressure pulse forcesthe plates outwardly, the lugs sliding freely over the tie-rods, to apoint of ex;

' pansion dependent upon the size of the charge and the eoinpressihilityof the dense fill material and the earth. The disengagement of tie-rodsfrom the lugs, of course, is preven ted by the stops. After the internalpressure pulse; is dissipated, the dense fill, having a densityexeeeding that ofthe liquid within the liner, expands againstthelinercausing' anexternal pressure which forces the plates' togetheruntil they arrive at substantially their original position. As isobvious,- the high-pressure forces generated by the explosionare'dissipated in compressing the dense fill and the earth against whichthe liner is expanded. Thus, the enormous forces which would crack,deform, or fragment a conventional structure are expended harmlessly inthe structure of the present invention.

The following example serves to illustrate a specific embodiment of thestructure of the present invention. However, it will'be understood to beillustrative only and not as limiting the invention in any manner.

Example A pit about 16 feet in diameter and about 12 feet in depthwasdugin the earth "The cylindrical liner (1O feet in diameter and 10 feet inlength) was of the form shown in Figures land 2 and was constructed froml6 curved steel plates each about 4 feet in width and 10 feet in length,the thickness of each plate being A1 inch. The tie-rods wereA-inch-diarneter steel rods, and the lugs were 3-inch x 3-inch inchsteel blocks welded to the plates and drilled to receive the tie-rods.The liner was suspended in the pit. In the annulus between the earthenwalls of the .pit and the outside of the liner poured dense, noncohesiv'e-fill material eonsisting of a mixture of about two parts of sandto one part of gravel, the fill material extending from the bottom ofthe pit to occupy a portion roughly approximate to one-fourth of thedepth within the liner. Then, water was introduced into the liner andseeped into the fill, the water level being slightly below, i.e. about 1foot below, the earths surface.

In testing this structure, numerous explosive charges weredetonated-below the surface of the water. The charges .varied in weightup to twenty pounds, and in no shot did any damage occur. to thestructure. In the shot made with the 20-pound charge, the liner expandedfrom its original diameter of about 10 feet to a diameter of about 12feet but returned int-act to its original shape and size. In contrast,a" water-filled solid steel shell /2 inch thick and 10 feet in diameterwill be permanently deformed, i.e. expanded irreversibly, by theunderwater detonation of a At-pound charge. I

As has" been illustrated, the liquid-filled structure of the presentinvention may be exposed over and over again to the forces from thedetonation of an explosive charge. ln'order to provide such a reusablestructure,

. the use of a reversibly expandable liner within an earthen To eachside of the cen- .pit and the use of noncohesive derisefill arecritical. 8'] means of this combination, the enormous pressures from thedetonation, which would act detrimentally against a conventional rigidsteel tank, are expended harmlessly by working against the liner and thecompressible. fill and earth. Because the liner is reversibly expandableand thus can move readily when high internal and external forces areapplied to it, no damage to the liner is incurred. The dense noncohesivefill, which absorbs most of the energy from the explosion, presentsduring the duration of the internal pressure pulse a uniform backingagainst which theliner' expands, which uniform backing, in contrast tomany types of earth, prevents distortion'or rupture of the liner. Whenthe internal pressure is dissipated, the fill material flows back freelyagainst the liner, forcing it inwardly.

The exact arrangement of the rigid elongated elements of the reversiblyexpandable liner is not critical so long as the elements overlap'topresent a continuous laminar surface when the liner is in the normalposition. The two illustrated embodiments of the liner construction areeasily fabricated and are eflicient in operation. Therefore, these formsconstitute preferred embodiments of the liner of the present invention.The exact form of the movable guiding and retaining means, or fasteners,used 'aso is not critical, the only requirement of the fasteners beingthat they are capable of moving freely to' permit unhampered expansionof the rigid elements. The combination of lugs and tie-rod exemplifiedQOIISll? tutes the preferred fastener, since these components arereadily available and simply installed and yet at the same time allowthe necessary movement. The substitution of other forms of a movablefastener, however, is completely Within the scope of the presentinventiorn For example, a coil springcould be attached to the lugs 153of Figure 1 and threaded through lug 9, or the spring could be attachedto lugs 9 and 10 of Figure 3.

A wide variety of materials of construction may be used for both therigid elements and the fasteners. The prime requisites'to be consideredin the selection Of the material for the rigid elements. are that it beof sufiicient strength to support the assembled liner and of sgfiicienttoughness to resist shattering due to the explosion forces. Any ductilemetal will serve adequately as the material of construction of the rigidelements. For minimum cost and simplicity of construction, I prefer touse steel, for example standard steel plates, as the material of therigid elements. Therefore, for ease of assembly, the use of steel forthe fasteners, e.g. the lugs and tie-rods, is preferable.

The dimensions of the liner, and also the pit, are dictated to someextent by the size and configuration of the explosive charges to betested or used in the structure. For example, a structure of relativelysmall overall dimensions is adequate when the charges employed aresmall, i.e. of a few pounds or less, whereas when larger charges areemployed, the structure correspondingly must be larger. Although theexact ratio of pit diameter to liner diameter is not critical, 1 havefound that the annulus of fill material between the liner in normalposition and the pit walls generally should be at least 2 feet in width,in order to supply the proper uniform backing for the liner. Thereby,the pit generally should have a diameter at least 4 feet greater thanthe liner diameter.

As afore-mentioned, the use of standard steel plates in the linerconstruction simplifies fabrication. The exemplified plates were 4 feetin width, but, of course, elements of greater or lesser Width may beused depending on the over-all size of the structure, which aspreviously explained is to some extent dependent upon the size of thecharges used. The only factor limiting the width of these elements isthat they must not be so narrow as to unlap during expansion of theliner. The thickness of the rigid elements of the liner naturally isgoverned by the principles upon which the construction of a cylindricalstructure is based. The liner must have rigid elements of a certainminimum thickness to withstand the external pressure resulting from thedifference in density between the material outside the liner and thatwithin the liner. For example, when the rigid elements are of steel, theratio of the thickness of the rigid elements to liner diameter (I.D.)must be at least about 1 to 1000. Hence, due to the two-layerconstruction of the liner, the ratio of maximum Wall thickness to linerdiameter (I.D.) must be at least 1 to 500. The larger this ratio, thethicker and stifier the wall will be and the more durable the structure.Thus, only economic considerations limit the extent to which this ratiois increased. When other materials of construction, e.g. aluminum, areused, handbook values of course are available for the determination ofthe wall thickness required.

As is obvious, with the exception of the afore-d-escribed generalrequirements, the exact dimensions of the liner components and thespecific construction material are not essential to the presentinvention but are selected on the basis of practicality as governed bythe fundamental principles of engineering.

The composition of the fill material is dictated by two essentialproperties. That is, the fill material must be of greater density thanthat of the liquid within the liner, and, secondly, this material mustbe noncohesive, ie it must not be permanently compressed during theexpansion but must be capable of flowing freely back against the linerand settling firmly against it after the expansion. A wide variety ofdense, noncohesive aggregate materials fit the above-listedprerequisites and, thus, can be used satisfactorily as the fillmaterial. Although the exact composition used, therefore, is notcritical to the present invention, experiments have shown a mixture oftwo parts of sand and one part of gravel gives excellent results, and,thus, on an economic basis, the use of this com sition is preferred.

A bottom-less liner, rather than a tank, has been purposely employed inthe structure of the present invention. Thereby, no deformable obstacleis placed in the path of that portion of the pressure pulse travelingdownwardly. In most cases, the liquid lost from the pit through seepageinto the earth is negligible, and, in any case, some replacement of theliquid during use is required. In very porous soil, excessive seepagemay be arrested by adding fine sand, coal ashes, oatmeal, or the like tothe dense fill material. Thus, the absence of a bottom in the linerconstitutes no drawback.

For economics, availability, and satisfactory performance, water in mostcases will be used as the liquid filling the liner. However, otherliquids, e.g. a glycol, act in a similar manner, and the use of theseother liquids is equally feasible.

Although the invention has been described in detail in the foregoing, itwill be apparent to those skilled in the art that many variations arepossible without departure from the scope of the invention. I intend,therefore, to be limited only by the following claims.

I claim:

1. A reusable explosion-resistant structure for the testing and use ofexplosives which comprises a pit in the earth, a reversibly expandablecylindrical liner disposed in said pit, said liner consisting of aplurality of rigid overlapping elongated elements interconnected inlaminar form by a plurality of spaced, movable guiding and retainingmeans, noncohesive fill material occupying the annulus between theearthen walls of said pit and the outside surface of said liner andextending from the bottom of said pit to occupy a portion of the spacewithin said liner, and a body of liquid disposed within said liner andsaid pit, said noncohesive fill material having a density greater thanthat of the filling liquid.

2. A structure according to claim 1, wherein the rigid elements of saidcylindrical liner are arranged in two layers such that a gap separatesthe lateral edges of adjacent elements in each of said layers, said gapsin one layer of said rigld elements being positioned near the center ofsaid rigid elements in the other layer.

3. A structure according to claim 1, wherein said rigid elements of saidcylindrical liner are so arranged that every element on both itsexterior and interior surfaces contacts another rigid element, saidsurfaces of the central portion of each of said elements remaining freeof contact with any other of said elements.

4. A structure according to claim 1, wherein said movable guiding andretaining means consists of a plurality of centrally apertured lugsthrough which is threaded a tie-rod.

5. A structure according to claim 1, wherein said rigid elements andsaid movable guiding and retaining means are of a ductile metal.

6. A reusable explosion-resistant structure for the testing and use ofexplosives which comprises a pit in the earth, reversibly expandablecylindrical liner disposed in said pit, said liner consisting of aplurality of rigid, overlapping, elongated steel elements interconnectedin laminar form by a plurality of spaced, movable guiding and retainingmeans, the ratio of the thickness of said rigid elements to the innerdiameter of said liner being at least 1 to 1000, noncohesive fillmaterial occupying the annulus between the earthen walls of said pit andthe outside surface of said liner and extending from the bottom of saidpit to occupy a portion of the space within said liner, and a body ofliquid disposed within said liner and said pit, said noncohesive fillmaterial having a density greater than that of the filling liquid.

7. A structure according to claim 6, wherein said liquid is water.

8. A structure according to claim 6, wherein said fill material is a 2/1mixture of sand and gravel.

References Cited in the file of this patent UNITED STATES PATENTS1,427,166 Parton Aug. 29, 1922 2,699,117 La Prairie Jan. 11, 19552,798,633 Cornell July 9, 1957

